Systems for the analysis of movement of persons are becoming increasingly widespread in the biomedical field, notably for analyzing the physical activity of a person.
The detection of the walking activity of a person provides information which makes it possible, for example, to estimate an energy expenditure of a person, to evaluate a level of sedentariness of a person, or to estimate the quality or loss of functional capacity after a surgical intervention or a medicinal treatment.
A document entitled “Ambulatory system for human motion analysis using a kinematic sensor: monitoring of daily physical activity in the elderly,” Biomedical Engineering, IEEE Transactions on, vol. 50, no. 6, pp. 711-723, June 2003, by Najafi, B., Aminian, K., Paraschiv-Ionescu A., Loew, F., Bula C. J., and Robert, P., describes a 2A1G movement sensor (a biaxial accelerometer and monoaxial gyrometer that is worn on the trunk of a person and of which the vertical acceleration signal is filtered by a 0.62-5.00 Hz band-pass filter). At least three evenly-spaced occurrences of peak amplitude higher than a threshold are sought on this filtered signal. It is difficult to set a universal threshold a priori, which notably involves a lack of reliability of such a system.
A document entitled “Reference data for normal subjects obtained with an accelerometric device”, Gait & Posture, October 2002 Vol. 16, Issue 2, Pages 124-134, by Bernard Auvinet, Gilles Berrut, Claude Touzard, Laurent Moutel, Nadine Collet, Denis Chaleil, and Eric Barrey, describes a frequential analysis of a walking activity considered to be a substantially periodic activity, which creates a power peak at a frequency that depends on the walking speed. The study of the ratio between even and odd harmonics of the vertical acceleration signal makes it possible to study the stability of the walk. This does not involve detecting a walking activity, but analyzing or characterizing a walking activity of a person when it is already known that the person is walking.
The document entitled “Classification of waist-acceleration signals in a continuous walking record”, Medical Engineering & Physics 22 (4) (2000), pp. 285-291, by M. Sekine, T. Tamura, T. Togawa and Y. Fukui, describes the use of a wavelet transform to distinguish, in a signal representative of the walk of a person, whether the latter is walking on a horizontal surface, climbing stairs or going down stairs. The content of this document does not make it possible to detect a walking activity.